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Human COL2A1-directed SV40 T antigen expression in transgenic and chimeric mice results in abnormal skeletal
K S Cheah1, A Levy, P A Trainor
1Department of Biochemistry, Hong Kong University.
Abstract:
The ability of SV40 T antigen to cause abnormalities in cartilage development in transgenic mice and chimeras has been tested. The cis-regulatory elements of the COL2A1 gene were used to target expression of SV40 T antigen to differentiating chondrocytes in transgenic mice and chimeras derived from embryonal stem (ES) cells bearing the same transgene. The major phenotypic consequences of transgenic (pAL21) expression are malformed skeleton, disproportionate dwarfism, and perinatal/neonatal death. Expression of T antigen was tissue specific and in the main characteristic of the mouse alpha 1(II) collagen gene. Chondrocyte densities and levels of alpha 1(II) collagen mRNAs were reduced in the transgenic mice. Islands of cells which express cartilage characteristic genes such as type IIB procollagen, long form alpha 1(IX) collagen, alpha 2(XI) collagen, and aggrecan were found in the articular and growth cartilages of pAL21 chimeric fetuses and neonates. But these cells, which were expressing T antigen, were not properly organized into columns of proliferating chondrocytes. Levels of alpha 1(II) collagen mRNA were reduced in these chondrocytes. In addition, these cells did not express type X collagen, a marker for hypertrophic chondrocytes. The skeletal abnormality in pAL21 mice may therefore be due to a retardation of chondrocyte maturation or an impaired ability of chondrocytes to complete terminal differentiation and an associated paucity of some cartilage matrix components.
Insights
Simian virus 40 (SV40) T antigen expression in cartilage cells caused skeletal malformations and dwarfism in transgenic mice. This suggests T antigen disrupts chondrocyte differentiation and matrix production, leading to developmental abnormalities.
Area of Science:
- Developmental Biology
- Genetics
- Molecular Biology
Background:
- Cartilage development is crucial for skeletal formation.
- SV40 T antigen is a viral protein known to affect cell proliferation and differentiation.
- Targeted gene expression allows investigation of specific protein functions in developmental processes.
Purpose of the Study:
- To investigate the role of SV40 T antigen in cartilage development.
- To determine if SV40 T antigen expression in chondrocytes causes skeletal abnormalities.
- To analyze the effects of SV40 T antigen on chondrocyte differentiation and extracellular matrix production.
Main Methods:
- Generation of transgenic mice and chimeras using COL2A1 regulatory elements to target SV40 T antigen expression to chondrocytes.
- Phenotypic analysis of skeletal development, including dwarfism and malformations.
- Assessment of chondrocyte density, collagen gene expression (alpha 1(II), alpha 1(IX), alpha 2(XI), type X), and aggrecan mRNA levels.
Main Results:
- Transgenic mice (pAL21) exhibited severe skeletal malformations, disproportionate dwarfism, and perinatal death.
- SV40 T antigen expression was specific to chondrocytes, driven by the COL2A1 promoter.
- Reduced chondrocyte density and alpha 1(II) collagen mRNA levels were observed.
- While some cartilage genes were expressed, chondrocytes in pAL21 chimeras showed disorganized proliferation and failed to express type X collagen, indicating impaired maturation.
Conclusions:
- SV40 T antigen expression in differentiating chondrocytes disrupts normal skeletal development.
- The observed abnormalities are likely due to impaired chondrocyte maturation and terminal differentiation.
- This disruption leads to reduced cartilage matrix components and skeletal defects.